KIDNEY AND SKIN AS EXCRETORY ORGANS. 863 



The inorganic salts of urine consist chiefly of the chlorids, phos- 

 phates, and sulphates of the alkalies and the alkaline earths. It 

 may be said, in general, that they arise partly from the salts ingested 

 with the food, and are eliminated from the blood by the kidney 

 in the water secretion; and in part they are formed in the destruc- 

 tive metabolism that takes place in the body, particularly that 

 involving the proteins and related bodies. Sodium chlorid occurs 

 in the largest quantities, averaging about 15 gms. per day, of 

 which the larger part, doubtless, is derived directly from the salt 

 taken in the food. The phosphates occur in combination with cal- 

 cium and magnesium, but chiefly as the acid phosphates of sodium 

 or potassium. The acid reaction of the urine is usually attributed 

 to these latter substances. The phosphates result in part from the 

 destruction of phosphorus-containing tissues in the body, but 

 chiefly from the phosphates of the food. The sulphates of urine 

 are found partly in an oxidized form as simple sulphates or con- 

 jugated with organic compounds, as described above. 



Micturition. The urine is secreted continuously by the kid- 

 neys, is carried to the bladder through the ureters, and is then at 

 intervals finally ejected from the bladder through the urethra by 

 the act of micturition. 



Movements of the Ureters. The ureters possess a muscular coat 

 consisting of an internal longitudinal and external circular layer. 

 The contractions of this muscular coat form the means by which 

 the urine is driven from the pelvis of the kidney into the bladder. 

 The movements of the ureter have been carefully studied by Engel- 

 mann.* According to his description, the musculature of the ureter 

 contracts spontaneously at intervals of ten to twenty seconds (rab- 

 bit), the contraction beginning at the kidney and progressing 

 toward the bladder in the form of a peristaltic wave and with a 

 velocity of about 20 to 30 mms. per second. The result of this 

 movement should be the forcing of the urine into the bladder in a 

 series of gentle, rhythmical spurts, and this method of filling the 

 bladder has been observed in the human being. Suter and Mayerf 

 report some observations upon a boy in whom there was ectopia 

 of the bladder, with exposure of the orifices of the ureters. The 

 flow into the bladder was intermittent and was about equal upon the 

 two sides for the time the child was under observation (three and 

 a half days). 



The causation of the contractions of the ureter musculature is 

 not easily explained. Engelmann finds that artificial stimulation 

 of the ureter or of a piece of the ureter may start peristaltic con- 



* "Pfliiger's Archiv f. die gesammte Physiologic," 2, 243, 1869, and 4, 33; 

 see also Lucas, "American Journal of Physiology," 17, 392, 1906. 



t "Archiv f. exper. Pathologic und Pharmakologie," 32, 241, 1893. 



